There are few events quite as awe-inspiring as the thunderous take-off of a spacecraft. Great clouds of fire gather underneath, billowing out from all sides, which seem to lift this man-made vehicle into the sky until it is but a faint dot. As it nears 29,000 km/h (18,000 mph) it eventually breaches our atmosphere – and it’s here that the outer space journey really begins.
But for all the ferocious power and speed of a NASA take off, there is an important part of the journey that we rarely see. At 5.6 km (3.5 miles), it pales in comparison to a round-trip to the moon, which is an absolute minimum of 356,500 km (221,500 miles), and at a sedate speed of less than 1.6 km/h (1 mph), it is almost the exact opposite of a space launch. But make no mistake about it, no trip to the moon, or visit to the International Space Station can begin without a painfully slow journey sat onboard a machine of colossal dimension.
NASA’s Crawler Transporters, officially named CT-1 and C-T2 but nicknamed Hans and Franz, really need to be seen to be believed. They are the largest self-powered land vehicles in the world and each one weighs an astronomical 2,712 tons – that’s about a quarter of the Eiffel Tower or 17 Statue Liberties, without their bases. Size is everything with these monsters but who can blame them when their most frequent passengers were the Space Shuttles which weighed in at a hefty 2,000 tons and measured 56 metres (184 ft) from nose to engine exhausts.
Countdown to Launch
If you’re a little unfamiliar with space launches you might be a little confused as to what exactly a Crawler Transporter is and maybe even why I’m getting so excited about them. No doubt many have seen a space shuttle launch. There’s a tower, there’s a spaceship, there’s a countdown, there’s a lot of fire – it all seems to happen quite quickly. But what we see is only a fraction of what happens in the build-up to a launch.
Firstly, whatever is going into space is not assembled on the launch pad. This takes place in NASA’s Vehicle Assembly Building (VAB), one of the largest buildings in the world, standing at 160.3 metres (526 feet) with a volume of 3,665,000 m3 (129,428,000 cubic feet) – which is 40 times that of the Albert Hall.
The VAB is 5.6 km (3.5 miles) from Launch Pad 39A and 6.4 km (4.5 miles) from Launch Pad 39B and it’s here that the sections of the spacecraft, along with additional fuel boosters, are carefully assembled. What we see nicely prepared on the launch pad as mission control counts down to zero has to be painstakingly constructed beforehand a short distance away.
Now, I say short distance, but considering what needs to be moved, this is the spacecraft equivalent of running a marathon up Mt Everest. Once assembled, the Crawler slides beneath the Mobile Launch Platform (MLP) on which the spacecraft now sits, before carefully lifting everything up and ever so slowly making its way to one of the launch pads, where it carefully places the MLP and its space cargo down.
In terms of Apollo-era machinery still in use, you’d be hard-pressed to find much, that is of course, except for the two giant Crawlers. In the early 1960s, NASA explored several ideas relating to how to move an incredibly tall and absurdly heavy structure like the Saturn V rocket with it all ending in tears.
They toyed with rail and canal plans but were drawn to the enormous earth moving machines used in mines at the time and after a rough design had been drawn up, NASA opened up the project for bidding. The lowest bid came from the Marion Shovel Company, located in Marion, Ohio and after winning the contract it set about building two identical Crawlers.
In July 1965, CT-1 underwent its first test. It successfully moved an umbilical launch tower around (1.6 km) 1 mile but engineers were initially stumped when they found various pieces of metal lying around the crawler. Eventually, it was found that bearing races, rollers and retainers from the crawler’s traction-support roller assembly had shed while moving and the design was sent back for reevaluation.
It didn’t take long to iron out the issues and in January 1966, CT-1 performed the same test again, this time without shedding anything. On 26th August 1967, the first operational Saturn V rocket, part of the unmanned Apollo 4 mission, was transported by Crawler onto a launch pad at the Kennedy Space Center and on 9th October 1968, the first manned mission, Apollo 8, again used a Crawler to make the journey between the VAB and the launch pad.
In those days, a single Crawler operation required between 20 and 30 people, half onboard, tending to the various mechanical aspects, and half walking next to it to make sure nothing else went wrong. Even today, between 15 and 20 engineers and technicians are required to make sure that the short but very slow trip goes smoothly.
Now, I don’t think we really need to go into any more detail over individual flights, because these two Crawlers have handled absolutely all of them and if I’m very honest there’s only so much you can say about a big machine that picks up another big machine and moves it. But to put their use in perspective, NASA estimates that both crawlers together have covered a huge 3,000 km (2,000 miles) – not bad for machines that typically move less than 1 miles per hour.
For nearly 50 years, the large lumbering figures of NASA’s crawlers have made their way slowly back and forth from the Vehicle Assembly Building at the Kennedy Space Center in Florida to various launch pads on site. Essentially their role in a successful space mission is short and almost entirely unheralded but these vast machines are mind-boggling and are certainly some of NASA’s unsung heroes.
As I mentioned earlier, they are the world’s largest self-powered land vehicles. While several machines are bigger, mostly large-scale excavators, they all run on external power sources. NASA’s Crawlers on the other hand come with their own engines and propulsion systems.
Let’s get the numbers out of the way first. They are 40 metres (131 ft) in length and 35 metres (114ft) in width – making it slightly bigger than a baseball diamond. Their height is adjustable depending on what is on it and varies between 6 and 8 metres (20 – 26ft), while they can carry a frankly ridiculous 9,000 tons, equal to twenty fully loaded 777 aircraft.
But it’s not all about huge numbers. Using its sophisticated computing system, this hulking giant can position and dock its platform on the launchpad to within half an inch of where it needs to be, while the person driving it can shift the entire structure by as little as an eighth of an inch.
Moving the Monster
The Crawlers come with two V16 ALCO 251C diesel engines pumping out 2,750 horsepower, which drive two 1,006 horsepower generators used for jacking, steering, lighting, and ventilating and which also power 16 traction motors.
At each corner of the Crawler is a set of tracks, with each track coming with 57 separate ‘shoes’ measuring 2.2 metres (7.5 feet) long, 0.4 metres (1.5 feet) wide and weighing 900 kg (1,984 lb). Meaning every single shoe included on the Crawler weighs roughly the same as two horses, and there are 456 shoes.
Somewhat ironically for such a giant mass of steel, the steering wheel is only around 15 cm (6 inches) in diameter. While driver input is certainly important, the majority of the technical aspects of the drive are controlled by an onboard computer – humans are good, but perhaps not good enough to be trusted to balance a structure over 25 storeys high. The journey is aided by a laser guidance system and giant jacking, equalization, and levelling (JEL) cylinders at each corner, which keep the entire structure stable at all times.
But it’s not just the mechanical giant above that has been carefully configured. The tracks that the Crawler and its cargo travel across have also been carefully constructed – and when you think about what travels above it and how much it all weighs, it’s easy to see why. A fully fueled space shuttle, complete with its boosters, external tanks and mobile launch platform (MLP), weighs in at a monstrous 6,000 tons. Now let’s add on the weight of the crawler and we get to roughly 8,700 tons – which is around three-fifths of the entire weight of the Brooklyn Bridge in New York.
Now, you can’t transport this kind of weight on a normal road, it would simply crack and then sink. The Crawler tracks have been designed to withstand such enormous weight by having various carefully constructed layers that go down to around 9 metres (30 ft).
It starts with 1.8 metres (6 ft) of roadbed, including around 0.8 metres (3ft) of crushed stone. The remaining 7.3 metres (24 ft) has been carefully settled and compressed to provide some of the flattest most stable ground you are ever likely to find. But this also needs to be constantly maintained and assessed. The weight above is so much that when the Crawlers pass over, its tracks essentially grind the top layer of rock into a fine powder. As I mentioned earlier, there are numerous people involved in a single trip and one of the key jobs is to constantly spray the crawl ways with water to avoid excess dust.
If you’re wondering about time, well, it takes in the region of 6 to 8 hours to make the single journey between the VAB and a launchpad – which certainly puts rush hour traffic in perspective doesn’t it? This is done with a relay of drivers who swap every hour or two
Crawling into the Future
When the Crawlers were first built they cost $14 million ($116.8 million today). Now, that’s not loose change, but considering these machines have been used constantly for over 50 years, a period where countless vastly more expensive vehicles have come and gone, it seems like an absolute bargain.
And what’s more, NASA expects to be able to use them for at least the next couple of decades. In recent years we’ve started to see a resurgence of interest in space travel and with NASA’s next-generation Space Launch Shuttle (SLS) nearing completion and scheduled for its first launch in November 2021, one of the old workhorse crawlers has undergone an upgrade.
CT-2 has seen its load capacity increased and upgrades were made to include larger, redesigned roller bearings and their lubrication system as well as larger JEL hydraulic cylinders. The onboard generators have also been increased in power and a new, large braking system has been installed. To top it off, a brand new Cummins V16 twin-turbo diesel engine has also been added. CT-1 has not received the same level of upgrades, and will only be used for non-SLS loads from now on.
When CT-2 arrives at the VAB in November and loads the new Space Launch Shuttle, which many hope might even allow us to travel to Mars one day, it will be, in many ways, just another day at the office for this giant machine. These behemoths moved the Saturn V rockets at the dawn of NASA’s space adventure, the Space Shuttle series over thirty years and now the next glorious chapter in the story.
When space vehicles blast off from the Kennedy Space Center they are embarking on journeys of astonishing lengths, speeds and complexities. But it all begins with a slow, tiny, yet epic journey on the back of one of NASA’s monstrous unsung heroes.